Optical system and method



' June 27 1944. D. R. LlGI-l 2,352,234

OPTICAL SYSTEM AND METHOD Filed Feb. 25, 1941 4 SheetSSheet [rzvenZ'orDAVID R.LIGH

6y 7&2 aiiarne ys DISPLACEMENT June 27 1944.

D. R. LHGIHI 511F114 OPTICAL SYSTEM AND METHOD Filed Feb. 25, 1941 4.Sheets-Sheet 2 2O 6O '70 BO DEG- ROTATION Tic fi.

lizverzar DAVID R. LIGH )zzis a'ai-orizeya' June 27, 1944. D. R. LIGHOPTICAL SYSTEM AND METHOD Filed Feb. 25, 1941 4 Sheets-Sheet 4 X w J 35O 32 I ,i Y J) r/ 221 I W I\ \a lizv eniar Tiqlll DAVID R. LIGH 2 2221saiivrzzeys Patented June 27,

or'rrcsr. srs'rms sun un'mon David a. Ugh, New Deep, N. Y2,

Industrial Management,

ford, Conn.

amignorto-Darli a Hart- Application February 25, 1941, Serial No.380,541

16 Claims. (Cl. as-icsi This invention relates to an optical system and7 method for recording or portraying motion, in which either the objector the image projected therefrom is held in a stationary location whilethe conjugate is moving constantly; and more specifically the inventionrelates to motion picture projectors or cameras using a constantlymoving film, or other apparatus embodying optical rectiflers. The objectof the invention is to produce a practical method and means of divertingthe light rays passing between an object and an image. the system beingof the type employing planar retracting means to cause therectification. It is characteristic of the invention that a plurality ofplanar retracting media are employed together so as to compensate forthe sine ratio characteristics of the light displacement for eachseparate medium, giving a net displacement otthe rays which is linear inrelation to the rotation thereof and in synchronism with the uniformmovement of the moving object or image.

In the drawings:

Fig. 1 is a geometric diagram of the retraction of a ray by a planarretracting medium such as can be used in the present invention;

Fig. 2 is a similar geometric diagram illustrating the parallel butdisplaced condition of the ray as it leaves the retracting medium;

Fig. 3 is a sheet of graphsillustrating the sine ratio character of thedisplacement of a light ray caused by rotation of a planar retractingmedium, and the compensating efiect produced by the present invention'to make the rectification linear;

]'igs.4to'7 areaseriesotdiaeramsshowing the rotation of twoplanar'refracting media op rated in accordance with the presentinvention to illustrate the principle of compensated displacement of aray as used in a motion picture machine; Fig. 4 showing the displacementat 30 of rotation from the vertical position of the first re- Iractingmedium; Fig. 5, the displacement at 60 of rotation; Fig. 6, thedisplacement at 120 of rotation; and Fig. 7, at 150 or rotation;

Fig. 8 is a diagrammatic view in side elevation of the essential partsof a motion picture projector made in accordance with this invention;

Fig. 9 is a view similar to Fig. 8, of a preferred form of motionpicture projector made in accordance with the present invention; whileFig. 10 is a front elevation of the shutter blade of the projector ofPig. 9.

It has heretofore been known to attempt projection of a motion picturefilm moving constantly, i. e.. non-intermittently. and rectifying forthis continuous movement of the film by using a plane parallel plate orretracting prisms to retract the light to give the necessary opticaldisplacement to follow the film movement: but such efforts have revealeddefects in the resulting screen images and methods of producing themwhich until the present invention have been incurable. According to thepresent invention, a plurality of such platw. optical flats or planarretracting media are employed in such a manner and location as toproduce the necessary linear motion concurrently with the film movementby a compensating action which avoids the defects of the prior art.

Owingtotheiactthatthespeedoflightray's varies according to the mediumthrough which they pass. when a light my strikes the surface of anothermedium at an angle other than normal tothatsuriacaitisreiractedasshowninldg. l. lnthisflurethelightnylisshownentering a planar retracting medium ll, namely.lass, at an angle i from the normal N, H, and the glass beingdenserthanaintherayisretractedor benttowardthenmmalsothatitsangleri'romthe normal is less than the angle of incidence i.Theanglesiandrareknownastheanglesof incidence and refraction,respectively, and the ratio of their sines is constant and is called theindex of refraction. The ratio of the sines of air and any other mediumgives the constant which is the index of retraction for that othermedium. It is well known that in an optical flat or other glass havingtwo parallel surfaces, theretractedrayftwillbebentawayimmthe normal onentering the glass and towards the normal on emerging. to amounts suchthat the emerging beam will be parallel to the incident beamI.liowevenwhiletheem il sbeamwillbeparalleltotheorighialbeam,thereisalateral displacement D, as shown inFig. 2. Starting from this geometric premise. using glass with thepreferred index of refraction of 1.60483 and the thickness '1 of theplanar retracting medium as 1 inch, the displacement oi. the beam varieswith th incident angle i in accordance with the following table:

Incident angle Displacement device, on the one hand, or a camera, ontheother; but it has not proved practical to vary the rate of angularturning of the planar refracting medium in accordance with thedisplacement curve to keep the rate of rectification of the projectedlight rays constant. I

As will now be described in an optical system according to the presentinvention, it has been found possible to compensate for the displacementcurve variation in the rate of rectification of the light beams so as toproduce a linear or constant rate of displacement of the light beamswhile rotating the planar refracting media at a uniform angular speed.Thus, although the dis-' placement in the prior art is not a linearfunction of the degrees of rotation of the retracting medium andtherefore the projected picture of a film frame moving at uniform ratehasv been iumpy," it has been found possible by using the presentinvention to reach the ideal, wherein the retracting medium turning withuniform anular rotation operates in a concurrent or synchronous relationwith th film moving at a constant speed across the aperture of the lightof the projector. The principle employed will be described withparticular reference to Figs. 4, 5, 6 and 7, which show the applicationof the prin-- ciple to a motion picture camera. Thus these figures showa ray of an image being diverted for presentation to the moving film. Byreversing the direction of the light ray, the figures would beapplicable to a motion picture projector.

A multiplicity of planar retracting media are employed in such a waythat they compensate and offset the non-linear psrtions of each otherwith the result that linear displacement, accurate well within practicallimits, is obtained from uniform angular rotation of the reiractingmedia. Basically it is necessary to have only two such media or plates,and the same have been identified in Figs. 4to '7 incl. as plates A andB, respectively. Each plate rotates on its own individual 18113 whichlies in a direction normal to therays. Both plates rotate in the samedirection, and in these figures it appears as counterclockwise rotation.The angle of incidence i for each position of the plate is indicatedbeside each figure, identified as M and 1B for the platoon and B,respectively, and there is also indicated the degree of rotation fromthe position in which plate A was vertical. When plate A is vertical,plate B is horizontal, for plate 13 is always in a position 90' behindplate A, with the same angular 90 relation maintained at all times.While 90' is the most effective compensating angle, and the constructionand calculations in the examples given are based on this angle, itshould be understood that compensation can be obtained from angles whichdiffer somewhat from 90". In other words, lines normal to the planes ofthe two plates are always at right angles to each other, with the secondplate through which the rays pass always lagging. It will be noted inFigs. 4 and '7 that the sun: of the angles of incidence equals 90 andthat this is true'for all positions of applicant's device. In order thatFigs. 4 to I may be properly considered with relation to the chartcomprising Fig. 3, it is noted that plate A starts at rotation at themidpoint on the left side of the sheet, which is the vertical positionof that plate, and at that time plate B is 90' rotated from thatposition. As shown in Figs. 4 to 7; the light beam coming from the otherelements in the optical system passes through first the left plate andthen the right plate before going to' the other main elements of theoptical system. The result of this successive passingthrough these twoplanar refracting media in succession gives the desired compensatoryeifect. By compensation broadly is meant that the displacement D causedby one plate always is in the opposite direction from the displacement Dcaused by the other plate. It is the particular net displacement from myapparatus which is used to synchronize or cause concurrent movement ofthe film and the projector. To explain this in more detail, a table isgiven here showing by plus or minus signs whether the displacement ofeach plate is above or below the original or incident ray at the variousangles of the two plates, as the rays, plates and displacements appearin Figs. 4 to 7.

Degrees rotation andialgebraic displacement s gn Incident angle DisplaceDisplm Plate A ment Sign Plate B ment in Actually it is found that thenet displacement, taking cognizance of these algebraic plus and minussigns, approaches so closely to a straight line (as shown in'Fig. 3) asto be well within the limits of tolerance of motion picture projection.(It might be noted that in passing through a cycle of 180 of rotation ofthe two plates, two

the ideal linear displacement and the extremely small deviation from theideal caused by this compensatory method.

U T Detyiation in arm rom Incident angle or angle 3 33 225? linearuniform of rotation 5 displacelinear ment displacement In the abovetable it will be noted that for a complete cycle of 90 rotation thetheoretical displacement D is two inches. It will be noted .that thedisplacements vary from minus 1 to tion of the plates. In such aprojector each picture frame is .30 inch high, and the displacement Dwill therefore be .30 inch for each cycle. In line of the table givenabove, the deviation from true linear displacement by the use of thesmaller plates will have as its maximum .00056 inch. Assuming that thepicture is magnified sixty times on the screen, this would introduce apossible picture jump of about of an inch. This is well within thelimits necessaryfor a steady picture.

With further reference to the refraction of the horizontal pencils oflight by the plates as shown in Figs. 4 to '7, it should be noted thatthe effective angles through which the combined plates may be rotatedare limited by several factors including (a) the aperture of theobjective lens; (b) the size of the picture frame; and (c) the movementof the film. Furthermore the effective angle of rotation is limited bythe size of the plates and the obvious fact that as the plane of a plateapproaches the direction of the incident beam, its refractiveeffectiveness is limited as it changes over to receiving the rays on its.other face. In this connection it should be noted that when the anglesof the plates are plus or minus 45 from the vertical, 1. e., 45 fromnormal to the rays, the net image displacement is 0. It has been foundthat in a practical design of 16 mm. projector under these variouslimitations, an angle of 38% out of each 90% is available for use, i.e., a light transmitting time efliciency of 42% can be obtained. Ashutter can be used to stop the light when it is not desired and also tointroduce a sufllcient number of alternate periods of light and dark toreduce the apparent fiicker."

The embodiment of my invention in the motion picture projector shown inFig. 8 will now be described. The central feature of the machine is therefracting or rectifying means, which in this case comprise two opticalflats" H and II. It should be understood that while I prefer to useplanar refracting media, such as optical flats,

' any refracting media which by uniform rotation will providedisplacement and compensate for each other so as to provide constant ortrue linear displacement, can be used. These refracting media willhereafter be referred to as plates. Iprefer to mount them in the machinewithout the intermediary of optical means such as converging ordiverging lenses between them. Each plate rotates about its own axis 13,ll, which axis is normal to the direction of the rays, the axesthemselves preferably lying at right angles to the direction of movementof the film. The plates have rotation relatively to each other, therotation being maintained so that the plates or their planar normals are90 apart at all times. The film IS in Fig. 8 moves downwardly and thetwo refracting plates II, I! therefore revolve in a counter-clockwisedirection, as indicated bythe small arrows. The plates are each mountedextending laterally from a gear wheel l6, I], re spectively, and aredriven in synchronism with the movement of the film by means of a largegear wheel 18, a small gear wheel 19, a worm!!! and the film motor 2|.The film I5 is given continuous linear movement by a sprocket wheel 22mounted on the same shaft with the gear wheels l8 and I9 and revolvingin synchronism therewith, the film being led past the plates II, I! onthe side of an aperture plate 23 away from the plates and passing overthe guide rollers 24, 25 as it approaches and leaves the aperture plate.It will thus be seen that the speed of movement of the film I5 isaccurately synchronized with the rotation of the refracting plates ll,l2 and the parts are made of such dimensions and so arranged that in thecase of a 16 mm. projector,

as the film moves down the distance of one pic- A source of light '26 isindicated at the left of the figure, the diverging rays from this sourceof light passing through a converging or condenser lens 21 whichefficiently transmits the.

light through the optical system. This lens brings the rays into aconcentrated relation which is maintained preferably untilafter the rayshave left the refracting plates! I, I2. After the rays have left therefracting plates H, l2, they pass through the objective lens 28 whichfocuses the light on a screen 29. I

In the construction shown in this figure, there is a shutter locatedbetween the condenser lens 21 and the aperture plate 23 for the purposeof cutting on the light rays when either of the refracting plates is ina change-over position. In the construction shown it has been found thatthis results in having the light for about 42% of the time. The shuttercomprises a pair of plates 30 projecting laterally from the side of agear II, the two plates being arranged parallel to each other a distanceapart slightly greater than the opening of the aperture plate 23. The

gear 3| is driven by the gear it of the adjacent refracting plate II,and the widths of the plates 8| are such as to cover the aperture andcut off v the light for the desired period of time.

From the description just given it will be obvious that in the projectorof Fig. 8, as the plate ll revolves from the vertical position the netdisplacement of the two plates will move down, synchronized with themovement of the film. For each 90' of rotation, the film advances oneframe and the compensated net displacement rectifles the picture frameto a stationary image on the projection screen. An aperture plate It mayalso be provided between the objective lens 28 and screen 28, ifdesired, to cut off any rays outside the central picture.

A preferred form of shutter is shown in Figs. 9 and 10. In thisconstruction there is a single shutter plate 35 lying in a planeperpendicular to the rays of light which originate at the lamp and areprojected by the condenser lens. This shutter I! can be mounted on ashaft 32 which is an extension of the shaft carrying the main drive wormgear 20 so that its rotation can be accurately synchronized with therotation of the refracting plates. As can be seen in Fig. 10, theperipheral portion of the shutter, which is the portion lying in thepath of the light, consists of spaced blades ll, 34, there being foursmall blades 33 spaced apart a distance equal to their width, and a verymuch wider blade I4 spaced from the four narrow blades a greaterdistance. In the construction shown in Fig. 9, I prefer to revolve thisshutter ll once for each movement of the picture frame. This means thatthe shutter revolves four times for each complete revolution of theretracting plates II, II. Since there are five blades I3, it altogetherand a corresponding number of spaces between them, it follows that thelight is interrupted with a frequency of five times per frame movement,so that if the film moves at the rate of 24 frames per second past agiven point, these shutter blades interrupt the light 120 times asecond. I find that this arrangement of blades produces the minimumamount of flicker. It may be pointed out that the large blade I on theperiphery of the shutter is interrupting the light while one or theother of the refracting plates is revolving through any non-operatingposition or change-over, while the four small blades 38 are merely tobalance up or equalize the intensity of the light during the time thatthe image appears on the screen with relation to the dark period tominimize the "fiicker.

If the invention is to be embodied in a camera for taking motionpictures, the object rays of light are displaced by means of therevolving refracting plates to conform with the moving film, andthere isno necessity for balancing up the intensity of the light by the smallblades 33. The shutter arranges for the exposure of the film in regulartimed succession and in proper relation to the operative andnon-operative positions of the refracting plates. The principle of imagedisplacement by optical refraction utilizing the in-. vention abovedescribed can, as above intimated, be used not only in motion pictureprojectors and motion picture cameras of standard or high speedpersistence of vision is used to show the motion of a constantly movingobject, whether such ob- Ject be shown directly or through a series ofimages in a film, on the one hand, or on the other, in the case of themoving picture camera the projecting of the image on the moving illm.

or television projectors. It is applicable wherever I claim:

1. In an optical system, means maintaining light rays in a concentratedrelation, in combination with two efiective rotating planar refractingmedia adapted successively to cause displacement of the rays from theprojecting means, and means rotating the media at uniform angular speedbut at lag in angular relation to each other, whereby uniform lineardisplacement of the rays is obtained.

2. In an optical rectifier system, the combination of a plurality ofrefracting media each adapted to displace a ray of light in the samemanner, said two media being adapted to rotate each about its own axisbut at such relative angles that their displacements of the ray are incompensating phase, and obturating means synchronized to cut off therays when either of the media is at an inoperative angle to the ray.

3. In an optical rectifier system transmitting a series of images of anobject, or vice versa, where one is at a stationary location and theother at constantly changing location, the combination of two planarrefracting media and means rotating them in the same direction withuniform angular speed, with the planes of one medium at a 90 angle tothe other, whereby the displacement of light rays by one medium iscompensated for by the other and uniform linear displacement results.

4. In an optical system for obtaining a stationary image from a movingone, or vice versa, the combination of two planar refracting media withmeans rotating them in the same direction and with uniform angular speedbut with a 90 lag in the normals to their axes, whereby uniform lineardisplacement of the image received or projected is obtained.

5. In an optical system wherein uniform linear displacement of image isdesired at one end of the system, the provision of two planar refractingmedia mounted in successive relation to the light path, in combinationwith means rotating them in the same direction about separate axes andwith uniform angular speed but with a 90 lag in the normal axes of themedia, and a shutter to obturate the light rays intermittently.

6. In a method of operating an optical refracting system, the rotationof two planar refracting media each about its own axis but in the samedirection and with constant angular speed, holding their planar normals90 apart, whereby the linear displacement of rays passing through thetwo media is made uniform.

7. In a method of operating an optical refracting system containingrotating planar re fracting means, the steps of presenting rays to aplanar refracting medium while rotating same with constant angular speedand subsequently presenting the refracted rays to a planar refractingmedium at an angle 90 removed from the angle of the first incident ray,whereby the net linear displacement-of the double passage of the rays ismade uniform.

-8. In a motion picture projector, means advancing a film innon-intermittent or constant speed manner and two planar refractingmedia located successively in the path of the image rays, in combinationwith means giving uniform angular rotation in th same direction to themedia sesame 5 with a 90 lag between the normal axes of the two media,whereby uniform linear dishlacemeut of image synchronizeciwith. the filmmovement is obtained.

9. In an optical rectifier system, the QOmbiZlQ." tier; of two opticalflats whose inolices of reirac tion are in the order of 1.605 and whichare located successively in the path of the light rays, and meansrotating them at a uniform speed in the same angular direction but withtheir planar normals 90 apart, whereby the rays will. be cliverted frompositions having uniform linear dis placement to a stationary location,or vice versa.

10. in an optical rectifier system having" film and. relying onpersistence orvisiori, the com-= bination of two critical flats locatedsuccessively in the path of the light rays, and means to give thenormals of said. flats uniform angular rotation synchronized with thefilm movement, while maintaining the normals in ac relation to each.other, and shutter to ohturate the rays of light during change-overposition.

'11. In an optical rectifier system relying on persistence of vision, alens adapted to maintain. rays in concentratecl relation, and twooptical flats of about 1.8% liiclices of refraction arranged to receivethe rays successively from the lens, in combination with meansrotatihgthe flats at untform angular speerl alcout ti: ir separate outwith the planar normals maintained about 93 apart in corrirsensatirigrelation to ratio displacement curves, whereby the linear displace meritof the rays from the second. will be uniform.

12. in an optical rectifier system relying on persistence of ViSiOlfl,two optical lists oi about 1.605 indices oi street-ion arranges toreceive the rays successively i'rcii the lens, anti ro toting the flatsat uniform angular speeci about their separate axes but with theirplanar normals maintaiheti about 9% apart in compensating? relation asto shoe ratio curve characteristics of linear displacement or" the rays,whereby the linear displacement of the rays emerging irom the-second.that will be uniform, in combination with a shutter actor-atlas any rayspassing when one of the is at as luefifeetive angle.

13. In an optical rectifier system relying on the persistence of vision,two retracting plates having similar light displacement qualities andwhosetotal cycle displacement equals the sum of the thickness of the twoplates, in combination with in linear displacement of the rays isobtained.

14. in an optical rectifier system, two retracting plates having similarlight displacement quali= ties, in combination with means rotating theplates on ares normal to the path of the light ray and with. the platesat such relative angles that the sums of the angles of incidence of thelight rays at the two plates equals 90?, whereby the total cycledisplacement of the light rays is independent of the index of refractionof the 26 plates,

iii. In an optical rectifier system, two retracting plates havingsimilar light displacement qualities, in. combination with meansrotatingthe plates on axes normal to the path or" the light rays andwith the plates at such relative angles that the sums of the angles ofincidence of the light rays at the two plates equals so", whereby thecycle displacement of the light rays is oh the thicm ess of the platesand independent of the index oi refraction of the plates.

, 16. in an critical rectifier system,-two retracting plates havingsimilar light displacement qualities and whose total cycle displacemenequals the sum of the thickness or") the two plates, anal photographicfilm, in combination with means rotating the plates on axes parallel tothe plane oi the film at uniform. angular unidirectional speed, therelative angles of the two plates being such that the sums of the anglesof incidence a equal 90, and the glass in the plates having an index ofrefraction of about 1.605, whereby the intra-cycle displacement causedby said plates is meal-s uniformly linear and the cycle displacement ofthe rays is equal to the cyclic movement of the DAHD R.

